In the fabrication of semiconductor based devices (e.g. integrated circuits or flat panel displays), layers of material may alternately be deposited onto and etched from a substrate surface (e.g., the semiconductor wafer or the glass panel). As is well known in the art, the deposition of material layer(s) and etching of the material layer(s) may be accomplished by a variety of techniques, including plasma-enhanced deposition and etching. In plasma-enhanced deposition or etching, the actual deposition or etching of the substrate takes place inside a plasma processing chamber. During the deposition or etching process, a plasma is formed from a suitable source gas to deposit a material layer on the substrate or to etch areas of substrate that are unprotected by the etch mask, leaving behind the desired pattern.
The shrinking feature sizes and the implementation of new materials in next generation of device fabrication on larger substrate sizes have challenged plasma etch and plasma deposition processing equipments to maintain the uniformities or process results from centers to the very edges of substrates. The larger sizes of the substrates and the smaller device sizes result in larger numbers of devices close to the very edges of the substrates (or wafers). This makes controlling of processing results at the very edges of substrates very critical.
At the very edge of the substrate, the deposition or etching plasma non-uniformity increases due to a few factors. For example, during plasma etching, the etching by-product concentration at the substrate edge is different from the center of the substrate due to the lacking of etching by-product source beyond the substrate edge. The lower etching by-product concentration can affect the etching uniformity at the very edge of the substrate. In addition, the substrate temperature is different at the substrate edge. Conventional plasma etching system usually has a substrate cooling mechanism in the substrate support to cool the substrate during etching process to maintain the substrate at a certain temperature. The very edge of the substrate sometimes hangs outside the substrate support and does not receive the same degree of cooling from the cooling mechanism in the substrate support as the rest of the substrate. The different substrate temperature at the very edge of the substrate can also increase the etching non-uniformity at the very edge of the substrate. Additionally, the etching gas concentration at the very edge of the substrate is different from the etching gas concentration over the rest of the substrate due to overloading of etching gas at the very edge of the substrate. The overloading is caused by less etching gas being consumed by the etching process at the very edge of the substrate compared to etching gas being consumed over the rest of the substrate. This overloading of etching gas can also increase the etching non-uniformity at the very edge of the substrate. The RF coupling effect at the very edge of the substrate is also different from the rest of the substrate due to the edge of the substrate overhanging the support and also due to the different material used for the edge ring that surrounds the substrate support. The different RF coupling effect can affect plasma generation efficiency and density and therefore can increase the etch non-uniformity at the very edge of the substrate.
Although not affected by the same factors as plasma etching processes, plasma deposition processes also show increased edge non-uniformity. Typically, the edge non-uniformity affects up to 20 mm to 30 mm from the very edge of the substrate. The plasma uniformity within this region (20 mm to 30 mm from the very edge of the substrate) makes the deposition or etching uniformity much worse than the rest of the substrate, especially within about 10 mm to the very edge of the substrate. The poor edge uniformity renders the devices that are within about 10 mm to the very edge of the substrate non-usable.
In view of the foregoing, there is a need for a method and apparatus that provides an improved plasma processing mechanism to increase the process uniformity at the very edge of the substrate to increase device yield of semiconductor substrates.